Molded plastic articles are widely employed because they can easily be manufactured in various desired shapes by the use of molding techniques. Such articles, however, have some defects such, for example, as generally low rigidity, tendencies to be deformed and degraded when subjected to elevated temperatures, poor resistance to abrasion, and possible cracking, swelling and dissolving caused by some chemicals and solvents. Consequently, in some technical and industrial fields, there is no option but to employ, instead of molded plastic products, metallic products which are inferior because of the necessity for producing them by splitting or dividing the entire product into two or more component parts and combining them as by welding and the like.
For offsetting defects as noted above and recovering superior moldability of the plastics, such techniques as nickel or chromium plating as well as sputtering have been utilized in the prior art to form very thin protective films on the outer surface of the molded plastics. It is, however, very difficult employing the prior art practices to form such protective films in uniform thickness on the inner surfaces of the cavities in the molded plastics, especially for inwardly flared shapes inaccessible from the outside, and almost impossible to form such films as thick as from 0.3 to 0.7 mm. Moreover, it is completely impossible to apply reinforcing films or layers of ceramic or metallic material onto the inner surfaces of the cavities of the complicated shapes in the molded plastic articles because ceramic or metallic materials have very high melting points and may cause degradation of molded plastic articles when applied at high melting temperatures. Ceramic material is evaluated as very resistive material having superior properties, but is not fully utilized especially in combination with moldable plastic materials.